Single hung windows made today include locking systems to make them relatively secure in the fully closed position. A problem occurs when it is desired to lock the lower window partially open while preventing movement of such lower window from the outside.
Adjustable window and sliding door locks have been described. Examples include Savio, et al., U.S. Pat. No. 3,512,821 (1970), Means U.S. Pat. No. 3,698,754 (1972) and Yogi U.S. Pat. No. 5,217,267 (1993). Problems with these include difficult installation, including special tools in some cases. Special tools for operation is undesirable since they may not be available in an emergency.